I wasn't sure exactly where to post this but this seems like the most appropriate place.

Ok, so I usually leave my computer running 24/7 and I wake up to find that my computer has apparently crashed sometime during the night. Note that this problem is only occasional though. Sometimes it will do it a few days in a row and sometimes it won't do it for a while. Although when this problem occurs I will just be able to view the OSD on the monitor or the screen saver which is set to the default windows screen saver and the hard drive light will be on without even blinking at all. Therefore I'm forced to use the dreaded restart button on the case. I usually have AVG, SyncBack and Windows Defender run different times over night...all at different times of course but I doubt those are the problem. I try to keep my computer fairly clean, dust wise and spyware/virus ware wise. I also defragment my hard drive a few times a month and run Auslogics registry defrag and tweaktown reg cleaner occasionally. So, according to AVG, Windows Defender, Lavasoft Ad-Aware and Spybot S&D my computer should be virus/malware/spyware/etc. free. This has been an issue for a while now but I thought I might be able to fix it with updates, virus checks and running check disk at start up every now and then but obviously it hasn't helped. I have ran Spinrite 6.0 on the hard drive and it found no errors. Also, nothing is overheating. Does anyone know what might be causing this? I'll post some general information below but let me know what else you all might need to help diagnose the problem. Thanks.

Specs:
Windows XP Home Edition (SP3)
AMD Athlon 64 4000+ @ 2.75Ghz
ATI Radeon X850XT 545/1200Mhz 256mb
2GB G.Skill PC 3200 @ 458Mhz
OS Hard drive: Sata II Samsung 320GB 16mb cache
Backup hard drive: Sata I 80GB Western Digital 8mb cache
Motherboard: Epox 9npa+ nForce 4 ultra
PSU: 500 watt earthwatts

I know that's just the basic info there but let me know what kind of report you might need from a program to help. Thanks.

You might want to reverse bios to stock as a test. I had a mobo that crashed overnight regardless of what was running, but the bsod went away as soon as the bios default was loaded. You might also want to stress test your pc again since it may have been a while since it was tested. Parts can degrade overtime.

A very good automated maintenance for a home PC. I do more or less the same. A few more malware scanning, daily defrag & system drive backup. Basically, the next day the pc is ready for another day of abuse.

Start, run, enter eventvwr.msc and look for any system errors that occur about the time xp crashed. I call that the black box. It can give you cues to what might trigger the BSOD.

Hey auscanzukus, thanks for the reply.

Well it must have crashed again overnight because the only thing I could see yet again was the OSD display for the monitor. Note that I'm not getting a blue screen of death but just the OSD (On Screen Display) for monitor settings. It's not going into sleep mode...restarting the monitor doesn't do anything either. I've recently ran a stress test on my system using prime95 for quite a few hours and it was rock solid. I did open up eventvwr.msc to try to find an error when it crashed last night (well, actually early this morning) and the only error I could find under application overnight was "Windows saved user XXXXX\XXXXXXX registry while an application or service was still using the registry during log off. The memory used by the user's registry has not been freed. The registry will be unloaded when it is no longer in use.

This is often caused by services running as a user account, try configuring the services to run in either the LocalService or NetworkService account." This had a source of Userenv. I don't think that this is the problem though since it looks like the same exact warning was given at around 6:00pm yesterday and it didn't crash. It's odd because it usually only does this overnight.

I did find something interesting under the System section though. It's an Error that reads: "CRT invalid display type" that occurred about 2 minutes after the above error. It has a source of ati2mtag. Although this really can't be it since it just happened 20 minutes ago and I'm still running fine. It's driving me nuts. Any other ideas? Thanks.

Well I updated my graphics driver a few days ago and thought that finally may have fixed this problem but yet again when I turned my monitor on I was just able to see the OSD and my hard drive light on my case was staying on solid. Needless to say I had to hard restart again. Anyway, I took a few screen shots of the time period the problem had to occur. I would have saved it as a text file and posted it but it was too much of a mess. I thought this would be easier to read. I haven't ever looked at event viewer until this problem started but I'm pretty sure it's not 'normal' to have this many errors. Although most of which occur even when I'm using my computer but I never experience any problems besides when it apparently crashes/lock up overnight. Does anything stick out to anyone here that might be causing this? Thanks.